1. Field of the Invention
The present invention generally relates to antennas for reducing RF emission exposure to humans from hand-held radios and, more particularly, to antennas for reducing the electromagnetic emission hazards associated with cellular telephones.
2. Description of the Prior Art
In recent years there has been a proliferation of personal communication devices, such as, hand-held radios and particularly cellular phones. In addition, the next generation of personal communicators is anticipated to be even more pervasive than cellular telephones. Like all new technologies, the convenience of personal communication devices does not come without environmental consequences. Whether real or perceived, the headlines and recent medical reports have sparked fear and concern over the personal safety of users constantly exposed to electromagnetic RF emissions radiating from the antennas of their personal communication devices. Reports suggest that personal communication devices have been linked to head anomalies such as brain cancer, indicating the need to develop device designs for reducing harmful antenna emissions or at least diverting RF emissions away from the user's head and body.
Several designs have been proposed for cellular phones to reduce electromagnetic exposure. Most of these designs involve using some type of electromagnetic shield, such as, U.S. Pat. Nos. 5,335,366 to Daniels, 5,338,896 to Danforth or 5,336,896 to Katz. For example, Katz discloses an electromagnetic shielded jacket for encasing a cellular phone. Round openings are cut into the jacket immediately adjacent to the ear-piece and the mouth-piece to allow sound waves to freely pass. Doors are provided for allowing limited access to the control pad. After a telephone number has been dialed or some other control button depressed, the user can close the door to protect from any radiation that might be emanating from the control pad. Unfortunately, jackets such as this are cumbersome and not particularly compatible with the now popular flip-phone design where the mouth-piece is placed on a hinged door which flips closed when not in use to cover the control pad.
Furthermore, while the Katz jacket shields a user from RF emissions radiating form the body of the phone, a much greater health threat has been associated with the much higher emissions which radiates from the antenna. Katz addresses the antenna issue by installing atop the jacket a telescoping antenna which is hinged at the bottom so that it can be tilted away from the user's head. While this may reduce emissions to the head somewhat by swiveling the tip of the antenna away form the head, the base of the antenna remains the same distance from the head. This is unfortunate since the telescoping antenna is active and emits radiation along its entire length from tip to base. Furthermore, when the Katz antenna is swiveled away from the head, the tip and length of the telescoping antenna inadvertently move closer to the user's arm, shoulder, back or chest. Hence, swiveling the antenna accomplishes little more than partially displacing the health risk from one part of the body to another.
Other designs to reduce electromagnetic emissions to the user's head involve modifying the design of the antenna itself. For example, U.S. Pat. No. 5,231,407 to McGirr et al. discloses an antenna comprised of radiating patch elements completely inside of a portable telephone chassis. The near field of the antenna is such that radiation to the user's head is minimized. French Patent FR 2679086 to Matra Communications addresses the electromagnetic exposure problem by moving the telescoping antenna from the top of the hand set to the bottom. Again, while these alternate antenna designs may reduce exposure to the head, they inadvertently increase exposure elsewhere. In the McGirr et al. design, it seems that the user's hand or shoulder may receive elevated exposures. Similarly, in Matra Communications design, the user's neck and torso receive elevated doses of radiation. As a further drawback, for both designs, transmission and reception may suffer since a larger part of the user's body absorbs and blocks much of the antenna energy.